Japanese Patent Laying-Open No. 2009-33265 (PTL 1) discloses a charging system capable of charging a battery mounted on a vehicle from a power supply external to the vehicle. In this charging system, a commercial power supply is connected via a cable to a charging port for charging the battery mounted on the vehicle, and the vehicle-mounted battery can be charged by the commercial power supply. Further, the vehicle and the commercial power supply are each provided with a PLC processing unit, and communication can be performed via the charging port and the cable between the vehicle and a data processor for the commercial power supply (see PTL 1).